To keep tiles fiom warping, you need to be sure that they dry evenly.
Keep turning them, but turn them between two boards, like a sandwich you
keep flipping so as not to warp them by picking them up when they are
damp. Another good way to dry them when they are leather hard is to put
them on those plastic grid sheets that they sell for liight covers on
large flourescent lights. You know what I mean? Grid strips with holes
in between them like a checkerboard. Don't put a fan on them, and dry
them slowly with plastic over them.